Field of the Invention
When producing optical arrangements, in particular optical high performance systems, very strict requirements are imposed on the tolerances of the entire optical arrangement and the resulting permissible tolerances of the individual components.
Deviations of individual components from a theoretically ideal shape and an ideal optical behavior usually manifest in the form of a wavefront error of the beams that pass through the optical arrangement. Wavefront errors are two-dimensional or three-dimensional deviations of the wave fronts (loci of identical phase) from an ideal wavefront, such as for example an ideal plane wavefront (plane wave) or an ideal spherical wavefront (spherical wave).
Description of the Background Art
The manufacture and the use of individual components with narrow tolerance limits are complex in terms of production, result in many waste parts, require a high level of outlay in terms of measurement and are therefore expensive, and it is difficult to produce them in relatively large numbers.
One possibility for minimizing the production complexity of the individual components is the introduction of at least two prefabricated optical compensation elements into the beam path of an optical arrangement in order to compensate a wavefront deformation (=wavefront error), as is known for example from EP 0 823 976 B1. To this end, the wavefront error at the optical arrangement is measured using a wavefront measuring instrument. The optical compensation elements are chosen in correspondence with the measurement result. The disadvantage of this solution is the necessary provision of a number of optical compensation elements, the necessity for further elements in the optical arrangement, and the high assembling complexity and space requirement for the optical compensation elements.
Another approach is known from DE 102 58 715 B4. In the method for producing an optical arrangement in the form of an optical imaging system having a multiplicity of optical elements, which is disclosed therein, first the optical arrangement is assembled. In this case, the optical elements are arranged in their correct positions. Subsequently, the assembled optical arrangement is measured, and a wavefront error in the exit pupil or in a face of the optical arrangement that is conjugate therewith is ascertained in a spatially resolved manner. In a next step, at least one correction area that is provided as a correction asphere at least one of the optical elements is selected, and a topography and/or a refractive index distribution of the correction area is calculated, with which correction of the ascertained wavefront error for the optical arrangement can be effected. In order to be able to bring about the necessary changes in correspondence with the calculated topography and/or the refractive index distribution of the correction area, the at least one correction asphere is removed from the optical arrangement and processed in a spatially resolved manner. It is important here to return the correction asphere after complete processing to the correct coordinates, i.e. with the alignment and rotary position that were used in the calculation of the correction values (topography and/or refractive index distribution) so as to achieve the desired effect of the correction of the wavefront error. The compensating element corrects the sum of the errors of the individual optical elements.
One disadvantage of this procedure is that the optical arrangement first has to be in fact assembled, then partially disassembled and finally re-assembled, and if necessary calibrated again. As a result, additional work steps are necessary to produce the optical arrangement.
From a solution according to DE 10 2005 022 459 A1, a method for optimizing the quality of an optical system is known, which comprises at least two elements with optically effective surfaces (optical elements). A resulting specific wavefront error is ascertained from the individual optical elements or from groups of optical elements by determining deviations of an actual form of the surface shapes from a predetermined form, and subsequently the relevant specific wavefront error is calculated by way of computer. The only disclosed calculation rule is, however, here not suitable for field-dependent simulation of the specific wavefront errors. The expected total wavefront error of the optical system is predetermined by way of computer on the basis of the calculation results, and it is ascertained by way of which surface shapes the total wavefront error can be corrected, wherein the ascertained specific wavefront errors are taken as the basis. These ascertained surface shapes are formed on at least one surface, and only then is the optical system actually assembled. According to the procedure of DE 10 2005 022 459 A1, the wavefront errors are corrected in a field-independent manner. This approach is not expedient in field-dependent optical systems (for example projection lenses), since the wavefront error of a field point requires individual (=field-point-dependent) correction. According to DE 10 2005 022 459 A1, each wavefront error is corrected at the same wavefront (phase function), as a result of which the correction potential is not fully exploited.